As is done in other ansible modules, this adds the __main__ check
to the module so that the module code itself can be used as a library.
For instance, when testing the code.
The bigip_api method was changed in the module_utils function definition
to include the validate_certs option but the bigip_virtual_server module
was not updated accordingly. This patch updates the method so that the
error message below is not returned to the user
received exception: bigip_api() takes exactly 4 arguments (3 given)
